The invention is based on a priority application EP04292437.3 which is hereby incorporated by reference.
The present invention is related to the field of wireless communication networks, more particularly the handover procedures in WLANs, and concerns a method for improving such procedures, in particular terms of data losses and handover optimisation, as well as an access point and a terminal able to perform this method.
Wireless networks have generally a cellular structure and are therefore subjected to handover procedures, and thus necessarily encounter the problem of continuity of communication, especially in case of voice data. The critical phase of that aspect of the handover procedure is the determining of the right moment at which to execute the handover, especially as the used radio devices are single-frequency.
Presently, the wireless local area network (WLAN) standards IEEE 802.11a/b/g are experiencing a successful development. This success is drawn by two main types of networks: enterprise networks and hot spots, i.e., conference centres, railway stations, airports, hotels . . . .
In both environments, VoIP (Voice over Internet Protocol) and VoWLAN are becoming attractive technologies with the main goal to reduce the communication costs by merging data and voice networks. Offering session continuity between hot spots and cellular networks could make VoWLAN technology very interesting, for all voice applications and for telecommunication operators.
In this context, the handover between two WLAN cells at different frequencies is a critical subject because the handover time has to be drastically reduced in order to allow VoWLAN seamless mobility between two IEEE 802.11 cells.
Several proposed schemes to solve this problem are based on channel measurements on a different frequency by the access point (AP) or by the mobile terminal (STA).
Such measurements can, for example, concern the signal power or the signal to noise ratio. The results of such possible repetitive measurements are compared to the values of the equivalent parameter(s) of the presently used channel f1 in order to determine if the conditions for a handover are fulfilled.
Possible measurement mechanisms are for example described in IEEE 802.11 k (standard draft).
Nevertheless, making measurements on a different frequency may imply packet or frame losses on the original frequency when the measuring occurs on the other frequency, since radio devices are single-frequency.